qemu: Don't delete TLS objects unless TLS migration was requested

qemu: Don't delete TLS objects unless TLS migration was requested

Trying to delete the non-existent TLS objects results in ugly error
messages in the log, which could easily confuse users. Let's avoid this
confusion by not trying to delete the objects if we were not asked to
enable TLS migration and thus we didn't created the objects anyway.

This patch restores the behavior to the state before "qemu: Reset all
migration parameters".

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>